Electroacoustic transducer

ABSTRACT

An electroacoustic transducer includes an electroacoustic transducer element and inner and outer acoustical reflection plates respectively positioned within an exterior to the transducer element. The electroacoustic transducer element emits an acoustic signal, such as an ultrasonic wave, from both the inner and outer surfaces of the element by expansion and contraction oscillations caused by an electrical signal applied thereto. Similarly, the transducer element can generate an electrical signal by applying an acoustical oscillation thereto. The inner and outer acoustical reflection plates will reflect acoustic oscillations emitted from the inner and outer surfaces in an axial direction in such a manner that a variable range of directivity may be realized and a high acoustic output obtained. The acoustic reflection plates are provided at suitable inclined angles so that the phases of acoustic oscillations emitted in the radial direction from both the inner and outer surfaces of the cylindrically shaped element of the electroacoustic transducer will essentially coincide.

D United States Patent [15] 3,703,652 Noda 1 Nov. 21, 1972 1ELEQIROACOUSTIC Primary Examiner.|. D. Miller TRANSDUCER AssistantExamj'ner-Marlt O. Budd 72 lnventor: Masahlro Noda,Amagasaki,.lapan [73]Assignee: MitsublshiDenki Kabushiki Kaisha, [57] ABSTRACT Tokyo'japan Anelectroacoustic transducer includes an elec- [22] Filed: Feb. 22,1971troacoustic transducer element and inner and outer 130] ForeignApplication Priority Data Feb. 25, 1970 Japan ..45/l6082 [52] U.S. Cl..310/8.3, 310/96, 340/8 FT [51] Int. Cl. ..H04r 17/00 [58] Field ofSearch ..3 l0/8.2-8.7, 9.1, 310/94, 9.6; 340/10, 8, 8 PT [56] ReierencesCited UNITED STATES PATENTS 3,302,163 1/1967 Andrews, Jr. ..340/8 FT2,855,526 10/1958 Jones ..3l0/8.3 X 2,005,741 6/1935 Hayes ..340/8 FI3,325,779 6/1967 Supernaw et al ..340/8 FT 3,271,596 9/1966 Brinkerhoff..3l0/8.3 X

l a. M I

Appl. No.: 117,619

acoustical reflection plates respectively positioned within an exteriorto the transducer element. The electroacoustic transducer element emitsan acoustic signal, such as an ultrasonic wave, from both the inner andouter surfaces of the element by expansion and contraction oscillationscaused by an electrical signal applied thereto. Similarly, thetransducer element can generate an electrical signal by applying anacoustical oscillation thereto. The inner and outer acousticalreflection plates will reflect acoustic oscillations emitted from theinner and outer surfaces in an axial direction in such a manner that avariable range of directivity may be realized and a high acoustic outputobtained. The acoustic reflection plates are provided at suitableinclined angles so that the phases of acoustic oscillations emitted inthe radial direction from both the inner and outer surfaces of thecylindrically shaped element of the electroacoustic transducer willessentially coincide.

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PATENTEDNB I972 3.703.652

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PRIOR ART PRIOR ART PRIOR ART INVENTOR.

MASAH I R0 NO DA m i/1115a: a waE PATENTEBNDVZI m2 mvsmoa MASAHIRO NODAAN ELECTROACOUSTIC TRANSDUCER BACKGROUND OF THE INVENTION 1 Field Of TheInvention This invention relates generally to a transducer having acylindrically shaped electroacoustic transducer element which may beexpansion and contraction oscillated in the radial direction of thecylinder, and more particularly, to a transducer having two acousticreflection plates, one being within the cylindrically shaped transducerelement and the other being exterior thereto.

2. Description Of The Prior Art Conventionally, electroacoustictransducers used for ultrasonic impulse proof devices, substancemovement detectors, and the like have included a cylindrically shapedelectroacoustic transducer element and a single acoustical reflectionplate. The electroacoustic transducer element will emit an acousticoscillation when excited by an electrical signal and will generate anelectrical signal when excited by an acoustic or mechanical oscillatingsignal. In the prior art transducers, the single acoustic reflectionplate was provided on either the inside or the outside of thecylindrically shaped electroacoustic transducer element. Thus, with theprior art transducers, the acoustic oscillations emitted from the innersurface of the cylindrically shaped electroaeoustic transducer elementwould be of an opposite phase to that of the acoustic oscillationsemitted from the outer surface of the cylindrically shaped element. Inorder to eliminate the problem caused with the generation of oppositephase oscillations, in the past, the acoustic oscillations emitted inthe radial direction from either the inner surface of the cylinder orthe outer surface of the cylinder would be reflected in the axialdirection of the cylinder and the remaining portion of acousticaloscillations would be shielded with an acoustic shielding plate.

While somewhat satisfactory, one of the problems with using only theacoustic oscillations emitted from one surface of the cylindricallyshaped element was that only a small amount of acoustic oscillationcould be effectively utilized. Thus, the efficiency of the singlereflection plate transducer is rather low. Moreover, with the prior arttransducer using a single reflection plate, the range of directivity inthe axial direction of the cylinder for changes in the angle of theacoustic reflection plate has been too narrow.

SUMMARY OF THE INVENTION Accordingly, it is one object of the presentinvention to provide a new and improved unique electroacousticaltransducer having a high efficiency when an electrical signal isgenerated by exciting a transducer element from either an acoustic ormechanical oscillation.

It is another object of the present invention to provide a new andimproved unique electroacoustical transducer having a high efficiencyand a broad and variable range of directivity in the axial direction ofthe cylindrically shaped element thereof.

One other object of the present invention is to provide a new andimproved unique electroacoustical transducer wherein the acousticaloscillations emitted from both the inner and outer surfaces of thecylindrically shaped element thereof can be effectively utilized.

Briefly, in accordance with the present invention, these and otherobjects, are in one aspect attained, by the provision of anelectroacoustical transducer which utilizes a pair of acousticalreflection plates one mounted within a cylindrically shaped transducerelement and the other mounted exterior thereto such that the acousticoscillations emitted from both the inner and outer surfaces of thecylindrically shaped transducer element will be axially directed whenthe element is expansion and contraction oscillated by an electricalsignal. In a particular embodiment, the inner acoustical reflectionplate is of a conical shape and the outer acoustical reflection plate isa conical cylinder having a notched portion on the upper edge thereof.The angles of the two reflection plates are appropriately determined soas to increase the power of acoustical oscillation and to provide avariable sharp to broad range of directivity. Additionally, it ispossible to select a sectional shape of directivity by shielding a partof an acoustical reflection plate with an acoustical shielding plate.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of theinvention will be readily obtained as the same becomes better understoodby reference to the following detailed description when considered inconnection with the accompanying Drawings, wherein:

FIG. 1 is a view of a cylindrically shaped electroaeoustical transducerelement showing the various modes of oscillation thereof;

FIG. 2 shows a plane view and a longitudinal sectional view of aconventional prior art transducer having a cylindrically shapedelectroacoustical transducer element and a single acoustical reflectionplate therein,

FIG. 3 shows a plane view and a longitudinal sectional view of anotherconventional prior art transducer having a cylindrically shapedelectroacoustical transducer element and an acoustical reflection platetherein;

FIG. 4 shows a plane view and a sectional side view of one preferredembodiment of an electroacoustical transducer in accordance with thepresent invention; and,

FIG. 5 shows a plane view, a longitudinal sectional view taken along theline bb of the plane view, and a longitudinal section view taken alongthe line c--c of the plane view of an electroacoustical transducer inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to theDrawings, wherein like reference numerals designate identical, orcorresponding parts throughout the several views, and more particularlyto FIG. 1 thereof, wherein the modes of mechanical oscillation of acylindrically shaped electroacoustical transducer element of the presentinvention is shown and may be made of a porcelain of barium titanate,lead zirco-titanate, or the like. The electroaeoustical transducerelement 1 may be expansion oscillated in the direction shown by thearrows 2 and may be contraction oscillated in the direction shown by thearrows 3. It will be apparent that the cylindrically shapedelectroacoustic transducer element 1 will emit acoustic oscillations bycausing expansion and contraction oscillations when excited with anelectrical signal supplied by a proper source, and on the other handwill generate an electrical signal when acoustically or mechanicallyoscillated from a proper source.

Referring now to FIG. 2, a conventional prior art transducer is shown ina plane view (A) and in a longitudinal sectional view (B). Thetransducer includes the cylindrically shaped electroacoustic transducerelement 1, an acoustic shielding plate 4, and a conical acousticalreflection plate mounted within the transducer element 1. The acousticalreflecting plate 5 is shown as having an angle dz, for reflectingacoustic oscillations. The symbol P shows the direction of transmissionof the reflecting acoustic oscillations.

Referring now to FIG. 3, another conventional prior art transducer isshown in a plane view (A) and in a longitudinal sectional view (B).Here, the transducer again includes the cylindrically shapedelectroacoustic transducer element 1, and an acoustical shielding plate6. However, differing from the prior art transducer of FIG. 2, anacoustical reflection plate 7 is herein provided and the same is mountedexterior to the transducer element 1 and has an angle d), for reflectingacoustical oscillations therefrom.

In the conventional embodiments shown in FIGS. 2 and 3, the reflectionplates 5 and 7 may be made of any material having an acousticalimpedance such as a metal, for example, of copper, aluminum or the like,or a plastic or the like.

In the conventional transducers described above, it should be understoodthat since the same have only a single reflection means that theacoustic oscillations emitted from the inner surface of thecylindrically shaped electroacoustic transducer element 1 will be of aphase opposite to that of the acoustic oscillations emitted from theouter surface of the cylinder. Because of the oppositely phased producedacoustic oscillations, only those emitted from either the inner surfaceof the cylindrically shaped electroacoustic transducer element or thoseemitted from the outer surface of the cylinder may be effectivelyutilized with that portion of the acoustic oscillations not utilizedbeing properly shielded. Thus, for example, either the acousticaloscillations emitted from the inner surface or the outer surface of thecylinder 1 in the radial direction will be reflected to the axialdirection of the cylinder 1 by utilizing the acoustic reflection plate 5or 7, while the remaining acoustic oscillations will be shielded byusing either the acoustic shielding plate 4 or 6. Since the conventionaltransducers, as described above with reference FIGS. 2 and 3, onlyinclude a single reflection means and thereby may effectively utilizethe acoustic oscillations emitted from either the inner surface or theouter surface of the cylindrically shaped transducer element, but notboth, the efficiency thereof will be extremely low and thereby may notbe effectively utilized. Moreover, with the above described conventionaltransducers, the range of directivity in the axial direction of thecylinder is extremely narrow for changes in either of the angles 4), or(b, of the acoustical reflection plates.

Referring now to FIG. 4, one preferred embodiment of the presentinvention for overcoming the above described disadvantages of the priorart is illustrated in a plane view (A) and in a longitudinal sectionalview (B). The electroacoustic transducer of FIG. 4 includes a pair ofreflection plates 5 and 7, the first plate 5 being mounted within thecylindrically shaped electroacoustic transducer element 1 and the secondplate 7 being mounted exterior thereto. The inner acoustical reflectionplate 5 has an angle of a, of reflection and the acoustical reflectionplate 7 has an angle of o of reflection and the same again may be madeof a metal, plastic, or the like. It should be noted that the acousticalreflection plate 5 may be formed in a conical shape, but it should beunderstood that the same is not so limited and that, for example, theinclined straight lines of the reflection plate 5 may be of a roundednature. The outside or exterior acoustical reflection plate 7 may beformed of a conical cylindrical shape and again, the inclined straightline portions thereof may be rounded.

In the transducer of the present invention, the cylindrically shapedelectroacoustic transducer element 1 may be oscillated by an electricalsignal provided from a conventional source such that acousticoscillations are emitted from both the inner and outer surfaces of theelement 1. Again, the phase of the acoustic oscillations emitted fromthe inner and outer surfaces are initially opposite each other. However,with the present invention, the angle d5, of the inner acoustical reflection plate can be adjusted with the angle (1!): of the outer acousticalreflection plate so that a differential is provided between thetransmission path of the acoustical oscillations emitted from the innersurface of the cylinder and the transmission path of the acousticaloscillations emitted from the outer surface of the cylinder such thatthe phase of all of the acoustical oscillations emitted from thetransducer will substantially coincide with each other in the axialdirection of the cylinder. Accordingly, the magnitude of the usableacoustical oscillations is greatly increased and likewise the efficiencyof the electroacoustic transducer. Moreover, with the present invention,the directivity of the transducer can be varied over a wide range byproperly selecting the angle d2, of the inner acoustical reflectionplate and the angle d), of the outer acoustical reflection plate.

By way of particular examples of the above described embodiment of thepresent invention, the directivity was 10 of half value angle, when theelectroacoustic transducer element 1 had an outer diameter of 25 mm., aninner diameter of 21 mm., and a height of IO mm. The electroacoustictransducer element 1 was excited by a 40 kHz. electrical signal and theangle of the inner acoustical reflection plate 5 was and the angle d),of the outer acoustical reflection plate 7 was 50.

The directivity was also 10 of the half value angle when theelectroacoustical transducer element 1 had an outer diameter of 38 mm.,an inner diameter of 34 mm., and a height of 10 mm. Again, an electricalsignal of 40 kHz. was applied to the electroacoustical transducerelement 1; however, here the angle a, of the inner acoustical reflectionplate 5 was set to and the angle d, of the outer acoustical reflectionplate 7 was set to 45. Under the same conditions, when the angle d1, ofthe outer acoustical reflection plate 7 was set to a directivity of 10of the half value angle was obtained.

Referring now to FIG. 5, another preferred and alternative embodiment ofthe present invention is shown in a plane view (A), in a sectional view(B), taken along the line b-b of the plane view, and in a sectional view(C) taken along the line c-c of the plane view. In FIG. 5, the outeracoustical reflection plate 7 is beveled and the acoustical shieldingplate 8 is placed on top of the beveled portion as shown in FIG. 5(A).

It should now be apparent that in accordance with the present invention,acoustic or electrical oscillations emitted from both the inner andouter surfaces of the cylindrically shaped electroacoustical transducerelement thereof which are of opposite phase to each other can, by theprovision of a pair of reflection plates, be changed in the axialdirection such that the phases of the acoustic or electricaloscillations are made to coincide, whereby the power of usableacoustical or electrical oscillation is greatly increased. Moreover, itshould now be apparent that with the present invention the directivityof the acoustic or electrical oscillations can be readily changed byproperly selecting the angles of both of the acoustical reflectionplates thereof.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. Thus, forexample, although ordinarily the sectional view of extent of theacoustic or electrical oscillations emitted from conventionaltransducers is generally of a circular nature, it is possible to attainvarious shapes within the extent of directivity by properly shielding aportion of the transducer with an acoustical shield plate. Thus, forexample, instead of a circular shaped emission, a square, rectangular orthe like shaped beam may be obtained. Additionally, while the presentinvention has been illustrated to show the cmittance of an acousticaloscillation by exciting the transducer with an electrical signal, itshould be readily understood that the transducer could be utilized toemit an electrical signal by exciting the same with an acousticaloscillation. Thus, the transducer of the present invention can beutilized for receiving, as well as transmitting acoustical signals.Moreover, while the present invention has been described as emitting anacoustical signal of the ultrasonic type, the invention is not solimited and may be equally used for transmitting acoustical sounds inother ranges, such, for example, as in the audible range. It istherefore to be understood that within the scope of the appended Claims,the invention may be practiced otherwise than as specifically describedherein.

WHAT IS CLAIMED AS NEW AND DESIRED TO BE SECURED BY LETTERS PATENT OFTHE UNITED STATES IS:

1. An electroacoustical transducer comprising:

a cylindrically shaped electroacoustical transducer element,

a first conical acoustical reflection plate having a given acousticalimpedance mounted within said transducer element for changing thedirection of transmission of acoustical oscillations therefrom, and,

a second acoustical reflection plate having an acoustical impedancewhich is the same as said given acoustical impedance, said secondacoustical reflection plate mounted in said electroacoustical transducerabutting an exterior surface of said transducer element for changing thedirection of transmission of acoustical oscillations therefrom, saidfirst and second reflection plates having different respectivereflecting angles relative to said electroacoustical transducer elementfor producing different length transmission paths between saidtransducer element and said first and second reflection plates so thatthe phases of all of the acoustical oscillations reflected from saidfirst and second reflection plates will substantially coincide with eachother in the axial direction of the cylindrically shapedelectroacoustical transducer element.

2. A transducer according to claim 1, wherein said second acousticalreflection plate is a conical shape and is beveled at the upper edgethereof.

3. A transducer according to claim I, wherein a shielding plate ismounted to said transducer for shielding a part of said transducer tocontrol the acoustical directivity thereof.

1. An electoacoustical transducer comprising: a cylindrically shapedelectroacoustical transducer element, a first conical acousticalreflection plate having a given acoustical impedance mounted within saidtransducer element for changing the direction of transmission ofacoustical osciallations therefrom, and, a second acoustical reflectionplate having an acoustical impedance which is the same assaid secondacoustical reflection plate mounted in said electroacoustical transducerabutting an exterior surface of said transducer element for changing thedirection of taansmission of acoustical oscillations therefrom, saidfirst and second reflection plates having different respectivereflecting angles relative to said electroacoustical transducer elementand said first and second reflection plates so that the phases of all ofthe acoustical oscillations reflected from said first and secondreflection plates will substantially coincide with each other in theaxial direction of the cylindrically shaped electroacoustical transducerelement.
 1. An electoacoustical transducer comprising: a cylindricallyshaped electroacoustical transducer element, a first conical acousticalreflection plate having a given acoustical impedance mounted within saidtransducer element for changing the direction of transmission ofacoustical osciallations therefrom, and, a second acoustical reflectionplate having an acoustical impedance which is the same assaid secondacoustical reflection plate mounted in said electroacoustical transducerabutting an exterior surface of said transducer element for changing thedirection of taansmission of acoustical oscillations therefrom, saidfirst and second reflection plates having different respectivereflecting angles relative to said electroacoustical transducer elementand said first and second reflection plates so that the phases of all ofthe acoustical oscillations reflected from said first and secondreflection plates will substantially coincide with each other in theaxial direction of the cylindrically shaped electroacoustical transducerelement.
 2. A transducer according to claim 1, wherein said secondacoustical reflection plate is a conical shape and beveled at the upperedge thereof.